In hard or floppy disk drive systems, a read/write head is moved across a data storage disk so as to be positioned over a selected one of a large number of substantially circular, concentric tracks. The disks have magnetic coatings on the surfaces within the tracks to provide memories for bits of data which can be randomly accessed at high speed for either retrieving or storing data. The read/write head is mounted on the end of an arm of a pivot actuator carriage so as to be positioned at the desired track by an actuator motor.
Typically, in hard disk drive systems, a plurality of disks are stacked on a spindle and a corresponding plurality of magnetic heads are used to read or write on respective surfaces of the disks. The magnetic heads ride on a thin layer of air created by the spinning disk with the heads being in close proximity to, but spaced from, the disk surface. When power is turned off, the actuator carriage is driven to move the magnetic heads to data-free parking or landing zones on which they may rest without destroying information, which is recorded only in other areas of the disks. Because of the rapid movement of the actuator assembly, a device is needed to limit the deceleration of the pivoting arm, in case of error or loss of power, to minimize damage to the head at the distal end of the arm.
Generally, a crash stop is provided to limit further movement of the actuator carriage once it reaches its stop position in the parking zone. The crash stop is conventionally in the form of a spring, or often simply a piece of viscoelastic material, arranged to impact a portion of the proximal end of the actuator arm at each limit of travel. Due to the relatively small size of small form factor disks, it is a significant part of the design of the disk drive to precisely position the actuator carriage at its stop position so as to minimize the area of the parking zone, which is essentially wasted disk surface space since no information is recorded thereon.
When the disk drive is not in use, it is important to park and hold the magnetic heads in a position where they cannot be moved and accidentally damage the data stored on the disk. To hold the actuator assembly in place while the drive is not in use, a latching arrangement is typically provided. One common latching arrangement utilizes a selectively actuated solenoid to hold the carriage assembly in place. Such systems have drawbacks, including the need for supporting electronics, relying on moving parts, and typically occupy large spaces or detract from the balance of the carriage assembly. Various types of magnetic latches have been proposed, generally positioning two opposing poles of a magnet close to a plate on the rear end of the actuator assembly so that when the actuator nears the parking zone, the plate will be attracted by the magnet.
Several U.S. patents have disclosed ways to limit the size of the parking zone on a data disk by providing a crash stop comprising a preloaded spring, and also to hold the actuator in place in the parking zone by providing a magnetic latch assembly. U.S. Pat. No. 4,635,151 to Hazebrouck discloses a rotary actuator with a crash stop comprised of a preloaded metallic leaf spring. In U.S. Pat. No. 4,890,176 to Casey, et al., a crash stop and magnetic latch for a voice coil actuator is disclosed. In U.S. Pat. No. 5,023,736 issued to Kelsic, et al., another type of magnetic latch for a disk drive actuator is shown. In U.S. Pat. No. 5,034,837 to Schmitz, a further type of magnetic actuator lock for a small form factor drive is shown.
The force exerted by a purely elastic (spring force) crash stop is approximately proportional to its deflection, and the maximum deceleration experienced by the actuator and attached head is at the final point of travel when the spring force is greatest. Consequently, previous devices have preloaded the spring crash stop to decrease the amount of deflection needed to stop the actuator and thus decrease the size of the parking zone on the disk. Ideally, preloaded spring crash stops function to slow the actuator's rotation in a minimum space. However, the spring force cannot be too great as the deceleration of the actuator will damage the magnetic head just as if it were a solid crash stop. Thus, even preloaded spring crash stops must have a minimum distance of deflection to absorb the kinetic energy of the rotating actuator. It would be preferable to apply the maximum acceptable deceleration at a constant rate and thus stop the actuator in a shorter amount of time. Prior spring crash stops are inadequate in this respect.
With regard to the prior latch mechanisms, there are problems inherent in trying to provide an area contact between the attachment plate on the actuator and the magnetic poles of the latch mechanism. One problem is manifested in a widened or unfocused magnetic field around the latch mechanism which tends to draw the actuator to it prior to landing, or when still in operation. Such a field will tend to interfere with the normal operation of the disk drive. Another problem is the fact that any misalignment between the flat surfaces of the magnetic poles and plate of the actuator, resulting from inexact machining or assembly, creates certain air gaps therebetween which reduce the holding strength of the latch mechanism.
Another problem with prior art actuator designs has been the inclusion of metallic screws or bolts holding the actuator return flux cover plate to the base of the disk drive. These fasteners, along with other metallic leaf springs or crash stop assemblies, are necessarily disposed adjacent the actuator coil and between the poles of the actuator magnet. Thus, the magnetic flux path is diverted from the space through which the actuator coil moves and instead flows down through these elements around the periphery of the motor. Diversion of the flux path as such results in a reduced efficiency of the motor.
The present invention provides an apparatus which substantially overcomes the drawbacks associated with prior art rotary actuators.